Chap. 3,] Specific Manures. 35 



to particular fpecies of vegetables. This they infer 

 from the exiftence of ipecific manures, as foot for 

 faintfoiri, afhes for white clover, and fome others. It 

 does not fcem poffible, however, to draw a line of 

 .diftincliion j and if we reject the idea of a fpecific 

 nourifhment in general* we cannot admit it in parti- 

 cular inftances. 



In order to difcover whether plants have an aflual 

 power of diftinguifhing matters prefented to their roots, 

 a friend, who affifted me in compiling this part of 

 the work, made, among others, the following expe- 

 riment. 



A vigorous plant of mint was placed in a two- 

 ounce phial, filled with filtrated well-water, to which 

 were added four drops of a moderately ftrong folu- 

 tion of fal martis. On examining the plant the fol- 

 lowing day, no other effect was obfervedj than 'that 

 the very tips of the radicles were withered and black. 

 Four more drops of the folution were now added. 

 On the third day the appearances were the fame ; 

 and no new change taking place on the fourth, twelve 

 more drops of the folution were added. On the fifth 

 day the roots appeared of a yellowiih green colour, and 

 the top drooped very much. The larger leaves were 

 pretty much withered and blackened. The abforp- 

 tion of the water appeared to be in fome meafure 

 impeded, but not entirely prevented. On the fixth 

 'day the whole plant was withering very faft; the 

 roots became of a dark olive-green colour, and the 

 larger leaves were become very black, efpecially tho. 

 foot-ftalks and the projecting fibres. On the feventh 

 day the blacknefs had made ftill further progrefs, and 

 the plant was dead. A fufficient proof that fome of 

 the iron was abforbed by the plant, may be drawn 

 from the following circumftance its leaves when ma- 

 D 2 cerated 



